1. Field of the Invention
This invention relates, generally, to the art of analyzing laser beams. More particularly, it relates to the art of analyzing high power laser beams.
2. Description of the Prior Art
A conventional apparatus for analyzing a high power laser beam includes a rotating needle that acts like a knife edge. The rotating needle reflects a small sampling of the focused laser beam into a detector. The needle, as it is rotated, moves along an optical axis and measures the beam waist of a focused laser beam.
Primes GmbH sells a unit that is capable of measuring powers up to 10 kilowatts, CW. The unit requires careful alignment and takes many minutes to make a measurement. It is bulky and does not facilitate real time measurement in a production process.
Multiple patents, such as U.S. Pat. Nos. 5,064,284, 5,069,527, 5,078,491, 5,100,231, 5,214,485, 5,267,012 and 5,459,565, disclose methods of analyzing a multimode laser beam by passing it through a rotating knife edge followed by translating the focal point along the optical axis to a detector.
The drawback to this approach is that the apparatus is bulky and requires many moving parts. It therefore does not facilitate quick and real time analysis of the laser beam.
U.S. Pat. No. 5,329,350 discloses a method for analyzing a laser beam by attenuating the beam with a pair of wedges and a second attenuation assembly. The light is then passed through a lens and a series of partially reflective plates where the number of beams produced is two times the number of partially reflecting plates used and then directs the beam onto a detector to view multiple spots simultaneously.
This method requires quite a few optics and is generally limited to analyzing a laser beam with a long focal length lens. This limitation exists because stacking a series of plates limits the beam waist that can be measured and makes it difficult to fabricate thin plates that permit analyzing a beam with a focal length much less than about three hundred millimeters (300 mm).
The earlier inventions disclosed in the above-mentioned patents are not capable of analyzing the beam using all the optical components of a conventional material processing system. The prior art devices also require the laser beam to be measured off line.
U.S. Pat. No. 6,313,910 discloses a rotation of apertures that are displaced along the optical axis of the beam waist to be analyzed. This device is rather compact and permits a more real time measurement, but includes moving parts that slow the measurement process and offers no acceptable means of attenuation for analyzing lasers with powers in the tens of kilowatts.
Thus there is a need for an apparatus for analyzing high power laser beams that is small and free of moving parts, has a small number of optics, uses all the optical components of a conventional material processing system, and attenuates the beam in an acceptable manner so that the beam can be measured in situ.
However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art how the limitations of the art could be overcome.